The present invention relates generally to apparatus for cutting sheet material with a closed loop control and deals more particularly with a cutting system and related method using an expert system containing built-in application knowledge with real time monitoring of critical system parameters to control the system's cutting speed during cutting in order adapt the automatic controls to existing conditions and improve and optimize system performance.
It is well known to use automatically controlled cutting machines for cutting limp sheet materials used in garments, upholstery, and other items. Such machines conventionally derive information defining the articles or patterns to be cut from a marker. The marker is a closely arranged array of patterned pieces in positional relationship for cutting from a layup of sheet material. The contours of the pattern pieces which define the cutting paths to be followed by the cutting blade are the rough data which are utilized by the automatically controlled cutting machine in guiding the cutting blade, and such data is translated by the machine into machine commands by appropriate hardware. For example, the marker may be digitized to reduced the contours to point data and when the point data is processed through a computer or data processor to generate machine commands which translate the cutting blade and sheet material relative to one another. The marker data may be preprocessed and recorded for subsequent use in a cutting machine or the data may be processed during the cutting operation.
In most prior art cutting systems which are automated, the cutting operation is substantially fixed by pre-established programs and the marker data. Thus, the maneuvering of the cutting blade along a desired line of cut is controlled in accordance with relatively standard routines that have proven in general to be suitable for many cutting conditions but not necessarily all cutting conditions nor unanticipated conditions and certainly do not represent optimal cutting routines. For example, the standard cutting operation may not be suitable or may produced poor results with certain types of limp sheet material, with layups of substantial depths and even within a single layup displaying different cutting characteristics under different conditions. Improvements over earlier systems have been made which allow a degree of flexibility in the cutting program by allowing the person digitizing the marker to call for special cutting blade maneuvers such as yawing and reduced feed rates under limited circumstances and one such system is disclosed in U.S. Pat. No. 3,803,960.
U.S. Pat. No. 3,848,490 having the same assignee as the present invention discloses a closed loop control system for an automatically controlled cutting machine wherein a pressure sensor (as shown in FIG. 2) is utilized to detect previous cuts in the sheet material in the immediate vicinity of the cutting blade and corrective adjustment in the automatic blade control mechanism is made in response to feedback signals generated by the pressure sensor. The corrective adjustment may reduce the feed rate as the cutting blade passes the previous cut or the blade may be given yaw commands.
U.S. Pat. No. 4,133,235 assigned to same assignee as the present invention discloses an improved closed loop control system for an automatically controlled cutting machine wherein a pressure sensor is utilized to detect previous cuts in the sheet material in the immediate vicinity of the cutting blade and provide corrective adjustment in response to feedback signals generated by the pressure sensor. The corrective adjustments include reducing the feed rate as the cutting blade passes the previous cut or providing yaw commands which rotate the blade slidely out of alignment with the desired cutting path in the region of the cut.
Even with the attendant improvements made with closed loop control systems for automatically controlled cutting machines as described above, the setting of the system feed rate on such machines is a manual operation wherein the cutter operator is responsible for setting the feed rate at the beginning of a cut using a feed rate dial on the cutter's control panel. For the most part, the feed rate setting is a subjective decision made by the operator based on knowledge of the system, fabric composition, ply height and other variable parameters which influence the system performance. In addition, the feed rate setting may also require adjustment during the cutting process to account for changes in the operating conditions. For example, it may be necessary to change the feed rate setting to account for changes in the ply height in step lays or changes in vacuum level on automatic control cutting machines having a vacuum hold down to maintain the sheet material on the cutting surface of the cutting machine wherein the vacuum level drops off due to previous cuts. Generally, the adjustment of the feed rate during the cutting process is handled in one of two ways. The operator can closely monitor the system and change the feed rate at the appropriate time using the feed rate dial. A second alternative is to set the feed rate to accommodate the worst case scenario that the operator anticipates. For example, the operator may set the feed rate for the entire cut at a low enough rate to handle the highest ply in the step lay or to handle the expected vacuum level drops off at the end of a bite. The obvious disadvantage of such an approach is that the overall system throughput is substantially below par. Furthermore, the operator can select only a limited number of discrete, integral feed rates, for example 1-15. For example, an operator may set the feed rate to 8 after concluding that a feed rate of 9 would be too fast. In actuality, the optimal feed rate might be 8.5 or 8.7 and therefore, the potential throughput possible cannot be obtained.
It is believed that more meaningful information concerning the cutting operation can be derived continuously from the interaction of the cutting blade and sheet material and also through monitoring the critical system parameters to automate the feed rate setting and substantially eliminate the requirement of operator intervention. It is, therefore, a general object of the present invention to provide a closed loop method and apparatus for automatically finding the optimal feed rate setting for the "spread" when the cutting process begins and to automatically adjust the cutting speed during the cutting process to account for changing conditions without requiring operator intervention.
It is a further object of the present invention to monitor critical system parameters to set the feed rate at the highest possible level the cutting system can operate at without over exerting the system while reducing wear and tear and the likelihood of encountering cutting problems.
It is a yet further object of the present invention to provide diagnostic capabilities to monitor and enhance cutting system performances by continually updating the amount of information available to the expert system for making decisions in directing the cutting system operation.